I just turned 28, and started HRT at 27.
I've met 7 other trans-girls at my local support group who started transition somewhere between my age and about 33, who have all been on hormones for over a year and a half. (Some up to 6 years.) And out of those seven, six of them were completely passable and living full-time with pretty much no difficulty whatsoever. (The last one, unfortunately, got no results from HRT whatsoever.)
Granted, they do not look completely like cis-women. There are still some masculine features there. But they look female enough that it would be VERY hard for anyone to clock them based on appearance. (Voice, on the other hand, is a different matter, but that's a problem with trans women of all ages.)
That is about what you can expect at this age. Mid-20s is still well within the ideal range where you can expect great HRT results, Because you're still at your physical peak, and the body is in an ideal state of health and replenishment.